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Thomas Arithmometer

This is the oldest surviving example of the type of stepped drum calculating machine constructed under patents obtained by the Frenchman Charles Xavier Thomas of the French town of Colmar in 1820. Machines that could do arithmetic automatically were built as mechanical marvels in the 1600s on the design of mathematicians such as Blaise Pascal and Gottfried Leibniz. However, it was only with the introduction and improvement of the machine of Thomas that calculating machines became part of the world of practical calculation. The instrument was made for Thomas by the Parisian mechanician and clockmaker Devrine. Thomas arithmometers, as the machines were called, became the first commercially successful calculating machines.

The brass machine fits snugly in a wooden case covered with red leather and lined with green velvet. It has three levers that are moved back to enter digits on brass stepped drums. A fourth lever, to the left of these, is labeled Multiplication, and used to determine the number of times the stepped drums rotate. Hence in this early machine, Thomas attempted direct multiplication by a single digit. This feature would not be successfully used in calculating machines until the late 19th century.

In back of the digit levers is a movable carriage with a row of six pairs of windows. Beneath each pair is a button. The levers are labeled: Unités, Dixaines, and Centaines. The pairs of windows are labeled: Unité, Dixaine, Centaine, Mille, Dix Mille, and Cent Mille.

Beneath each window is a numeral wheel. Two sets of digits are marked on each wheel, one in black and the other in red. Shifting a lever on the right of the carriage to “add e multiplication” opens six windows to show in black digits the result of addition and multiplication problems. In the other positions, six windows open to show in red digits the result of division and subtraction problems. Beneath the windows are thumbscrews for zeroing the result digits one at a time. There is no revolution register.

Pulling a red ribbon operates the machine. Pulling a shorter ribbon attached to the front assists in removing it from the case. Later Thomas machines would be crank-operated. The lid of the case has a brass handle, lock, and key. Part of the right side of the case turns down to allow for the motion of the carriage.

A mark on the left of the levers reads: Arithmomètre (/) du Chr. Thomas de Colmar (/) Par Brevet d’invention (/) Devrine fecit. A mark on a button at the front of the machine reads: Régulateur. A mark on the top of the lid reads: ARITHMOMÊTRE (/) De MR. LE CHER THOMAS DE COLMAR.

The machine is not identical to that shown in the drawings of Thomas’s 1820 patent. It resembles the drawings made in 1821 for a report by Hoyau published in 1822.

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